An advantage of a hybrid drive in a vehicle is that an internal combustion engine can be operated in an advantageous efficiency range more frequently and for longer periods of time. When the vehicle is accelerated, the internal combustion engine and an electric machine can be operated jointly. During braking and during coasting of the vehicle, part of the braking energy can be recovered and stored in an energy accumulator. More particularly in urban traffic and during downhill driving, energy recovery contributes towards a reduction in fuel consumption. If no or only a small amount of driving power is required, the internal combustion engine can be switched off completely. This can be the case during coasting, under stationary conditions or when driving at low speed (e.g. when parking the vehicle) with a charged accumulator.
Usually, the internal combustion engine is drivingly connected to a multi-step transmission that transmits torque generated by the internal combustion engine to the driveline. In the case of motor vehicles driven by a rear axle only, the torque is transmitted by the multi-step transmission via a propeller shaft to a rear axle differential drive. The rear axle differential drive distributes the introduced torque to two output shafts for driving the wheels, with the two output shafts having a differential effect relative to one another, i.e., if one of the two output shafts rotates more quickly, the other one of the two output shafts rotates correspondingly more slowly, and vice versa. In the case of all-wheel drive motor vehicles, a central differential is connected downstream to the multi-step transmission so as to transmit part of the introduced torque to the rear axle and part of the torque to the front axle.
From DE 199 19 454 A1, a motor vehicle drive assembly is known with an internal combustion engine, a gear changing assembly and an electric machine. Via a cardan shaft, the internal combustion engine drives the rear wheels. The electric machine can be drivingly connected to the front wheels via a separating coupling and a driveshaft. The rotor of the electric machine is connected to the separating coupling via a connecting drive.
US 2006/0113127 A1 proposes a hybrid motor vehicle with an internal combustion engine, an electric main motor and an electric auxiliary motor. The electric main motor is arranged at the rear end of the multi-step transmission, with the output shaft of the electric main motor being drivingly connected to the output shaft of the multi-step transmission. The electric auxiliary motor is arranged so as to adjoin the internal combustion engine and is connected via a belt drive to the crankshaft. The two electric machines are each connected to a battery.
From DE 10 2008 037 886 A1, a drive assembly is known for a motor vehicle driven by a plurality of axles. The drive assembly comprises a transfer case which transmits torque introduced by a drive unit to a rear driveline and a front driveline. The rear driveline is permanently drivingly connected to the transfer case to be able to permanently transmit torque to the rear axle. The front driveline is optionally drivingly connected to the transfer case to transmit torque to the front axle.
Especially in the case of rear axle driven motor vehicles with a longitudinally arranged internal combustion engine, integrating an electric machine for a hybrid drive is frequently complicated because of the limited installation space available. In addition, there may be a need for expensive re-designing processes to be carried out on fixed components to which the hybrid drive has to be attached, as a result of which the number of variants and related costs are increased.